1. Field of the Invention
The invention relates to machine vision systems. More particularly, this invention relates to lighting systems for machine vision systems.
2. Description of Related Art
Machine vision systems have been in use for many years. These systems are designed to remove the human element from the manufacturing and inspection process. Many manufacturing and inspection operations are not necessarily difficult but they are boring. It is the boredom of these tasks that causes people to become unfocused during the operation, leading to defects in the product.
Vision systems traditionally have used monochrome or gray scale systems to capture the images of objects. These systems typically view the object through a video camera to determine particular attributes of the object. The system may be used to determine if a particular attribute is present or if it is properly oriented or located within a predetermined area. These systems may provide feedback during the manufacturing process or they may be used off-line as inspection devices or manufacturing aides. The feedback system may include a computer controlled feedback loop or it may be provided through human interaction. The scales of gray may be appropriate for determining some material attributes such as size, shape or color differences; however, when the degrees of differentiation between similarly colored parts is slight, a color system may be required. Thus, color recognition systems have also been incorporated into machine vision systems for more complex tasks. All of these systems rely on a sensory input device, typically a camera, a processor and a lighting device, to control the lighting of the object to be analyzed. The advent of powerful computing systems has allowed the development of the colored system. These color systems require more computations per second because of the complexity of the system. Many of these systems work on high-speed productions lines where any reduction in speed is intolerable, necessitating the need for increased computational power.
Lighting is a vital part of both the gray-scale and color systems. If the lighting does not create the proper contrast or color, the system will slow down, give false indications, or completely fail to operate. Several lighting systems are available for these vision system applications.
Vision systems typically require a light source with full visible-spectrum light emission. The light source produces light and the light is reflected off of an object to be inspected. The sensing system (e.g., camera) collects the reflected light and a processor analyzes the image for color and/or contrast. If the light source does not emit wavelengths compatible with the color of the object, the contrast between the targeted attribute and other attributes will be low. This low contrast can lead to false readings or false indications. To avoid such problems, vision systems generally use light sources that emit light throughout the visible spectrum. These light sources typically do not provide equal amounts of energy throughout the visible spectrum but they do emit some energy throughout most of the spectrum. In the case of an incandescent or halogen source, the red emission is high but the energy level is drastically reduced as the wavelength shortens, so there is very little blue emission. Fluorescent lamps tend to have gaps in the spectral output where there may be little or no emission. Once a light source is selected and the vision system is programmed, it is important that the lighting conditions remain constant. If the lighting conditions change, the reflected light and the resulting image may also change. Periodic calibrations may be provided to compensate for changing conditions within the light source.
There are several methods for analyzing the reflected light. One such method is referred to as the RGB or red, green, blue method. The RGB method involves representing all colors as a mixture of red, green and blue which constitute the primary colors used by video cameras, televisions, and PC monitors. When combined, these colors can create any color within the visible light spectrum. The second method is referred to as the HIS or hue, saturation and intensity method. HIS is based on how humans perceive color so the method is more intuitive than RGB. The method of data interpretation depends on the complexity of the task. Where coarse degrees of color separation are required, such as when identifying a red component from a green component, the RGB method may be chosen. Where the degrees of color are much finer, such as sorting pharmaceutical tablets or inspecting fruit, the HIS method may be used.
Many other methods of data interpretation and manipulation could be used or developed. Lighting is an integral part of all vision systems and it would be useful to have a lighting system incorporated into the vision system. It would also be useful to have the vision system communicate with the lighting system to create various effects.